A Bitcoin paper backup that follows best practice
One printable file, recording everything a recovery needs. Not just the seed words.
Funds are lost this way far more often than they are stolen
People back up the seed phrase and stop. A seed phrase alone is often not enough to find the coins. Recovery also needs the wallet configuration: the derivation path, the script type, the passphrase if you set one, and for multisig, every co-signer's extended public key.
That configuration usually lives only inside the wallet software. When the laptop dies, the app is discontinued, or someone else is doing the recovering, it is gone.
Four sheets per key, filled in by hand
Open it, print it, write on it. The document works offline from a local file and makes no network requests.
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Key identity
Master fingerprint, which device made the key, and the multisig index.
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Seed words
One letter per box, with the word number beside it so a misread letter cannot cost you.
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Passphrase
Optional. Discard the sheet if you do not use one.
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Instructions
Not secret. The handwriting key, the test log, and what your heir needs to read first.
For a single-signature wallet that is everything. For multisig you must also back up the wallet descriptor yourself, which keybackup does not supply. The guide explains how.
Open source
Read the source, check the document does what it claims, and change it to suit how you hold your keys. Corrections and translations welcome.